Hitler's bombers failed to destroy this East Anglian airfield: now nature engages in stealthy obliteration. The concrete track leading to the airstrip follows the line of the Roman road between Baldock and Godmanchester. Just a few years ago it was wide enough to accommodate two gambolling dogs.

On this first truly autumnal morning I find it has shrunk to a twisting single file. Stonecrop was the first invader, feasting on the lime. Moss soon provided a deep green carpet below the mat of fleshy leaves. Plantains and coarse grasses followed these tough pioneers. Now bramble stems snake over the crumbling surface and sprouting blackthorn bushes, breaking from the cover of the nearby hedge, are completing the conquest.

Just over 60 years ago Halifax and Lysander aircraft thundered along the broad main runway before lifting off into the night sky, carrying resistance fighters and supplies bound for occupied territory. Today a single hare lopes over the frost-cracked tarmac, whose edges erode year by year into the adjacent fields like broken bits of a stale biscuit.

My eye is drawn to the centre of this flat expanse, where a timber-roofed brick barn stands as the only memorial on this historic site. The concrete shelves lining the inside walls, where members of the wartime Special Operations Executive stored their parachutes, still survive largely intact, now bedecked in dusty wreaths of paper poppies, curling photographs of men in uniform and tiny cardboard crosses. The white spattering on the hard floor shows that birds use the barn too. Grey pellets on the topmost shelf remind me of the little owl which raised her brood here this summer. In 12 years of visiting this airfield we have never seen any evidence of vandalism. I like to think it is out of respect to the many courageous men and women who collected their equipment at dusk from this simple barn and never brought it back.

· A Lifetime of Mountains, the best of A Harry Griffin's Country Diary, is published by Guardian Books. To order for £12.99 plus p&p call 0870-836 0749 or visit theguardian.com/bookshop